fix(medcat-trainer): Postgres load_examples fails on unique constraint

[alhendrickson]

This was a long one, for a one line change.

.save gets called twice in models.py. I think for sqlite it doesnt care at all, but postgres fails.

This is only seen on load_examples as it calls /api/modelpacks/, but if you use the admin UI it all worked fine as it calls a different API.

I'm not 100% on the actual change if anyone with a bit more django knowledge has opinions. Basically it should just update the foreign keys instead of inserting again.

Bug

Application logs

2026-01-20T13:43:18.964957939Z [medcattrainer] Internal Server Error: /api/modelpacks/
2026-01-20T13:43:18.964993604Z [medcattrainer] Traceback (most recent call last):
2026-01-20T13:43:18.964999327Z [medcattrainer]   File "/usr/local/lib/python3.11/site-packages/django/db/backends/utils.py", line 105, in _execute
2026-01-20T13:43:18.965003517Z [medcattrainer]     return self.cursor.execute(sql, params)
2026-01-20T13:43:18.965007298Z [medcattrainer]            ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
2026-01-20T13:43:18.965011079Z [medcattrainer]   File "/usr/local/lib/python3.11/site-packages/psycopg/cursor.py", line 97, in execute
2026-01-20T13:43:18.965014962Z [medcattrainer]     raise ex.with_traceback(None)
2026-01-20T13:43:18.965018641Z [medcattrainer] psycopg.errors.UniqueViolation: duplicate key value violates unique constraint "api_modelpack_pkey"
...

2026-01-20T13:43:18.965969644Z [medcattrainer]     raise ex.with_traceback(None)
2026-01-20T13:43:18.965973323Z [medcattrainer] django.db.utils.IntegrityError: duplicate key value violates unique constraint "api_modelpack_pkey"
2026-01-20T13:43:18.966259155Z [medcattrainer] DETAIL:  Key (id)=(13) already exists.
2026-01-20T13:43:18.966264061Z [medcattrainer] ERROR 2026-01-20 13:43:18,956 log.py l:253:Internal Server Error: /api/modelpacks/
2026-01-20T13:43:18.966267842Z [medcattrainer] Traceback (most recent call last):
2026-01-20T13:43:18.966271214Z [medcattrainer]   File "/usr/local/lib/python3.11/site-packages/django/db/backends/utils.py", line 105, in _execute
2026-01-20T13:43:18.966274995Z [medcattrainer]     return self.cursor.execute(sql, params)
2026-01-20T13:43:18.966278470Z [medcattrainer]            ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
2026-01-20T13:43:18.966282047Z [medcattrainer]   File "/usr/local/lib/python3.11/site-packages/psycopg/cursor.py", line 97, in execute
2026-01-20T13:43:18.966285828Z [medcattrainer]     raise ex.with_traceback(None)
2026-01-20T13:43:18.966289302Z [medcattrainer] psycopg.errors.UniqueViolation: duplicate key value violates unique constraint "api_modelpack_pkey"
2026-01-20T13:43:18.966292675Z [medcattrainer] DETAIL:  Key (id)=(13) already exists.

Postgres logs

20 17:28:36.944 GMT [17471] LOG:  statement: INSERT INTO "api_conceptdb" ("name", "cdb_file", "use_for_training", "create_time", "last_modified", "last_modified_by_id") VALUES ('Example Model Pack_CDB', '/home/api/media/model_pack_vM3qHeH/cdb', true, '2026-01-20 17:28:36.943543+00:00'::timestamptz, '2026-01-20 17:28:36.943562+00:00'::timestamptz, NULL) RETURNING "api_conceptdb"."id"
2026-01-20T17:28:37.303Z | 2026-01-20 17:28:37.303 GMT [17471] LOG:  statement: INSERT INTO "api_vocabulary" ("name", "vocab_file", "create_time", "last_modified", "last_modified_by_id") VALUES ('', '/home/api/media/model_pack_vM3qHeH/vocab', '2026-01-20 17:28:37.302798+00:00'::timestamptz, '2026-01-20 17:28:37.302816+00:00'::timestamptz, NULL) RETURNING "api_vocabulary"."id"
2026-01-20T17:28:37.305Z | 2026-01-20 17:28:37.305 GMT [17471] LOG:  statement: SELECT "api_metacatmodel"."id" FROM "api_metacatmodel" INNER JOIN "api_modelpack_meta_cats" ON ("api_metacatmodel"."id" = "api_modelpack_meta_cats"."metacatmodel_id") WHERE "api_modelpack_meta_cats"."modelpack_id" = 23
2026-01-20T17:28:37.308Z | 2026-01-20 17:28:37.307 GMT [17471] LOG:  statement: INSERT INTO "api_modelpack" ("id", "name", "model_pack", "concept_db_id", "vocab_id", "create_time", "last_modified", "last_modified_by_id") VALUES (23, 'Example Model Pack', 'model_pack_vM3qHeH.zip', 12, 12, '2026-01-20 17:28:37.307383+00:00'::timestamptz, '2026-01-20 17:28:37.307410+00:00'::timestamptz, NULL) RETURNING "api_modelpack"."id"

2026-01-20T17:28:37.308Z | 2026-01-20 17:28:37.308 GMT [17471] ERROR:  duplicate key value violates unique constraint "api_modelpack_pkey"

2026-01-20T17:28:37.308Z | 2026-01-20 17:28:37.308 GMT [17471] DETAIL:  Key (id)=(23) already exists.

After fix

• It now calls update instead of insert

2026-01-20 17:46:02.316 GMT [19337] LOG:  statement: SELECT "api_metacatmodel"."id" FROM "api_metacatmodel" INNER JOIN "api_modelpack_meta_cats" ON ("api_metaca
tmodel"."id" = "api_modelpack_meta_cats"."metacatmodel_id") WHERE "api_modelpack_meta_cats"."modelpack_id" = 25
2026-01-20 17:46:02.318 GMT [19337] LOG:  statement: UPDATE "api_modelpack" SET "concept_db_id" = 14, "vocab_id" = 14 WHERE "api_modelpack"."id" = 25